Saturday, January 12, 2013

Why do dogs wag their tails?

Every dog-person knows that emotions are communicated via the tail.  But WHY dogs wag their tails, from a biological point of view, continues to be a mystery.  
Tail wagging is a fairly unique trait. Dogs do it. Wolves don't, at least not to excess. Part of the reason has to do with tail anatomy.

Wolves have bushy tails that 
they carry almost parallel to their backs.

Dogs, on the other hand, 
have tails of all shapes and sizes. 
 Read more about dog tail shapes here.

Dogs, wolves and coyotes have anal glands that secrete signature scents.    Another scent source is a gland on the outer part of the tail called the supracaudal gland. Course black guard hairs indicate its location.

This is what it looks like on a coyote.

Whether or not domestic dogs retained the gland during evolution remains unclear.  It's possible that some breeds have it and others don't.  Dogs with certain kinds of coats have a dark spot where the gland would be located. My dog Chance has the black spot. But I can't tell if he has the gland.  

Tail Waggers
Unlike their adult counterparts, wolf pups wag their tails.  Maybe the little guys don't have fully developed scent glands, so wagging is needed to amplify the odor and push the smell around. As they get older, scent glands become more developed. When wolf pups reach sexual maturity, tail wagging wanes. 

Why wag your tail when you can distribute 
your scent more efficiently by a rub and a rolicking roll.  

So why do dogs wag their tails?
Some evolutionary biologists believe that domestic dogs are wolf pups in dog clothing. As wolves changed to dogs, biological development was arrested in such a way that typical dog behaviors, like playing, ball retrieving, tail wagging and even barking, are left over remnants of wolf puppy behaviors.

Tail wagging is a behavior that's lost its original function through evolution.  Dogs wag their tails because they still can.

And that's a good thing.


  1. Mine does it when he is happy. When I say out, he starts wagging, lol. Now he cannot hear, so I notice he doesn't wag as much, but when he is outside, he gets some wagging in.


  2. I think the only time our dog doesn't wag her tail is when she's sleeping or knows she's displeased me. Otherwise it's like a perpetual spring waving gently back and forth in the air. When she finds a particularly fresh interesting trail, it lowers and starts wagging vigorously, and is accompanied by the "beagle bay".

  3. I googled this expecting to find conformation of my theory... when my dog wags her tail it usually hits my leg. I figured it had something to do with finding other pack members withought moving concentration off of the hunt.

  4. That's a really interesting theory. I'd never thought of it. Let me know what you find out.